Ram air turbine structures for temperature dependent damping

ABSTRACT

A ram air turbine (RAT) actuator includes a housing and a piston in operable communication with the housing and at least one damping orifice in operable communication with the housing and the piston, a flow area of the at least one damping orifice being alterable to adjust damping of movement between the piston and the housing in response to changes in viscosity of a fluid related to temperature.

BACKGROUND 1. Field

The present disclosure relates to ram air turbines, more specifically toram air turbine structures for temperature dependent damping.

2. Description of Related Art

The deployment of a ram air turbine (RAT) into the airstream iscontrolled by a RAT deployment actuator. This actuator is a storedenergy device, that when a locking mechanism (uplock) is released thestored energy of a spring to pushes the RAT out of its storage bay inthe aircraft and into the airstream. In order to control the impact atthe end of the actuator stroke the actuator is filled with hydraulicfluid. This fluid is housed in a piston volume that is swept duringdeployment. The hydraulic fluid in this volume is forced through aseries of damping/snubbing orifices. These damping orifices control andslow the rate of actuator extension at the end of the actuator's stroke.This reduces the impact forces at the end of the actuator stroke.

The RAT system has to supply power to the aircraft within a limitedamount of time. Due to this time requirement the damping orifice cannotover restrict the deployment resulting in a deployment time exceedingthe deployment time limit. However, if there is not enough damping theimpact force will exceed the structural capability of the system.Therefore the damping of the system has to be tuned based on the impactforce and deployment time limit.

The typical hydraulic fluid used in RAT deployment actuators is Skydrol.This fluid changes viscosity with temperature. Because of this change inviscosity the amount of energy required to push fluid through thedamping orifices changes drastically. This results in RAT actuators thatdeploy quickly when the fluid is warm, but at a much slower rate whenthe fluid is cold. The constraints on the design of the damping orificesthen become: 1) that the actuator must deploy quickly enough to meet thetotal RAT start-up time requirement when cold and 2) when hot thedamping must be sufficient to ensure the impact load is below that ofthe structural capability of the system.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for improved RAT structures. The present disclosure providesa solution for this need.

SUMMARY

A ram air turbine (RAT) actuator includes a housing and a piston inoperable communication with the housing and at least one damping orificein operable communication with the housing and the piston, a flow areaof the at least one damping orifice being alterable to adjust damping ofmovement between the piston and the housing in response to changes inviscosity of a fluid related to temperature. The housing can define ahousing cavity at least partially disposed within the housing cavity ofthe housing in a sealing relationship with the housing. The piston candefine a piston cavity therein and can be configured to allow thehousing to move axially relative to the piston between a deployedposition and a stowed position wherein hydraulic fluid can flow betweenthe housing cavity and the piston cavity. A plurality of dampingorifices can be defined in the piston.

The actuator can include a damping orifice blocking device disposedaround or within the piston and configured to allow or block flowthrough one or more of the damping orifices as a function oftemperature. The damping orifice blocking device can be configured toallow flow through one or more of the damping orifices when within afirst temperature range and to block the one or more damping orificeswhen within a second temperature range that is higher than the firsttemperature range.

The piston can be made from a first material and wherein the dampingorifice blocking device is made of a second material different than thefirst material. The second material of the damping orifice blockingdevice can thermally expand faster than the first material of thepiston. In certain embodiments, the damping orifice blocking device canbe aluminum and the piston can made of steel.

The piston cavity can be configured to contain the damping orificeblocking device therein. The piston can include a retaining structurewithin the piston cavity to retain the damping orifice blocking devicebetween the first and second temperature range. The damping orificeblocking device can be a ring or a bimetallic spring disposed within theretaining structure configured to expand radially to block the one ormore damping orifices when within the second temperature range.

In certain embodiments, the damping orifice blocking device can includea sheath disposed within the piston cavity and fixed at one end relativeto the piston such that the sheath can thermally expand axially relativeto the piston to block the one or more damping orifices when within thesecond temperature range. The sheath can include a plurality of sheathholes corresponding to the one or more damping orifices such that thesheath holes align with the one or more damping orifices when within thefirst temperature range and the sheath thermally expands to block theone or more damping orifices when within the second temperature range.

The piston can be configured to be fixed to an aircraft and the housingis configured to be moved relative to the piston. Any suitableconfiguration is contemplated herein.

In accordance with at least one aspect of this disclosure, a method forcontrolled damping of an actuator over a temperature range comprisesmodifying a damping orifice flow area of at least one damping orificewithin the actuator as a function of temperature to counteract viscositychanges of a damping fluid related to temperature changes. Modifying thedamping orifice flow area can include allowing flow through one or moredamping orifices of a piston when within a first temperature range andblocking the one or more damping orifices when within a secondtemperature range that is higher than the first temperature range.

In certain embodiments, blocking the one or more damping orifices whenwithin a second temperature range includes radially expanding a dampingorifice blocking device within the piston to block the one or moredamping orifices. In certain embodiments blocking the one or moredamping orifices when within a second temperature range can includeaxially expanding a damping orifice blocking device within the piston toblock the one or more damping orifices.

These and other features of the systems and methods of the subjectdisclosure will become more readily apparent to those skilled in the artfrom the following detailed description taken in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject disclosureappertains will readily understand how to make and use the devices andmethods of the subject disclosure without undue experimentation,embodiments thereof will be described in detail herein below withreference to certain figures, wherein:

FIG. 1A is a partial cross-sectional view of an embodiment of anactuator (e.g., for a ram air turbine) in accordance with thisdisclosure, show within a first temperature range and/or an extremethereof;

FIG. 1B is a partial cross-sectional view of the embodiment of FIG. 1A,shown within a second temperature range and/or an extreme thereof;

FIG. 2A is a partial cross-sectional view of an embodiment of anactuator (e.g., for a ram air turbine) in accordance with thisdisclosure, showing within the first temperature range and/or an extremethereof; and

FIG. 2B is a partial cross-sectional view of the embodiment of FIG. 2A,shown when within the second temperature range and/or an extremethereof.

DETAILED DESCRIPTION

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectdisclosure. For purposes of explanation and illustration, and notlimitation, an illustrative view of an embodiment of an actuator inaccordance with the disclosure is shown in FIG. 1A and is designatedgenerally by reference character 100. Other embodiments and/or aspectsof this disclosure are shown in FIGS. 1B-2B. The systems and methodsdescribed herein can be used to control actuator deployment speed acrossa range of temperatures (e.g., for ram air turbines).

A ram air turbine (RAT) actuator includes a housing and a piston inoperable communication with the housing and at least one damping orificein operable communication with the housing and the piston, a flow areaof the at least one damping orifice being alterable to adjust damping ofmovement between the piston and the housing in response to changes inviscosity of a fluid related to temperature. Referring to FIGS. 1A and1B, a ram air turbine (RAT) actuator 100 can include a housing 101defining a housing cavity 103 and a piston 105 at least partiallydisposed within the housing cavity 103 of the housing 101 in a sealingrelationship (e.g., via one or more seals 102 as shown that interactbetween the housing 101 and the piston 105) relative to the housing 101.The housing 101 and cavity 103 can include any suitable shape (e.g.,cylindrical). The piston 105 defines a piston cavity 107 therein and isconfigured to allow the housing 101 to move axially (e.g., right to leftas shown) relative to the piston 105 between a deployed position (e.g.,the housing 101 is moved left relative to the piston 105 as shown) and astowed position (e.g., in the position as shown in FIGS. 1A-2B).

While movement is described herein, the piston and housing movement arerelative to each other in any suitable manner. For example, the piston105 can be fixed to an aircraft structure and housing 101 can beattached to a RAT and moveable relative to the aircraft structure. Thereverse can be true as well.

A plurality of damping orifices 109 is defined in the piston 105.Hydraulic fluid can flow between the housing cavity 103 and the pistoncavity 107 through the damping orifices 109 to allow actuation betweenthe deployed position and the stowed position.

The actuator 100 includes a damping orifice blocking device 111 disposedaround or within the piston 105 and configured to allow or block flowthrough one or more of the damping orifices 109 as a function oftemperature. The damping orifice blocking device 111 can be configuredto allow flow through one or more of the damping orifices 109 whenwithin a first temperature range (e.g., as shown in FIG. 1A) and toblock the one or more damping orifices 109 when within a secondtemperature range (e.g., as shown in FIG. 1B) that is higher than thefirst temperature range.

The piston 105 can be made from a first material and the damping orificeblocking device 111 can be made of a second material different than thefirst material. In certain embodiments, the second material of thedamping orifice blocking device 111 can thermally expand faster than thefirst material of the piston 105. In certain embodiments, the dampingorifice blocking device 111 can be aluminum and the piston 105 can madeof steel. It is contemplated that the reverse can be true, and thedamping orifice blocking device 111 can be disposed outside of thepiston 105 and can be configured to shrink relative to the piston 105with an increase of temperature to thereby block one or more of thedamping orifices 109 when within the second temperature range.

As shown, the piston cavity 107 can be configured to contain the dampingorifice blocking device 111 therein. The piston 105 can include aretaining structure 113 within the piston cavity 107 configured toretain (e.g., axially in FIGS. 1A and 1B, radially in FIGS. 2A and 2B)the damping orifice blocking device 111 between the first and secondtemperature range. As shown, the damping orifice blocking device 111 canbe a ring or a bimetallic spring disposed within the retaining structure113 and can be configured to expand radially to block the one or moredamping orifices 109 when within the second temperature range. Theretaining structure 113 can include any suitable structure (e.g., innerflanges configured to fit a ring as shown in FIGS. 1A and 1B).

In certain embodiments, referring additionally to FIGS. 2A and 2B thedamping orifice blocking device 211 can include a sheath disposed withinthe piston cavity 207 and fixed at one end relative to the piston 205such that the sheath can thermally expand axially relative to the piston205 to block the one or more damping orifices 209 when within the secondtemperature range. The sheath can include a plurality of sheath holes215 a, 215 b corresponding to the one or more damping orifices 209 suchthat one or more of the sheath holes 215 a, 215 b align with the one ormore damping orifices 209 when within the first temperature range (e.g.,as shown in FIG. 2A) and the sheath thermally expands to block the oneor more damping orifices 209 when within the second temperature range(e.g., as shown in FIG. 2B). As shown, the one or more sheath holes 215b can be sized to allow fluid communication between one or more dampingorifices 209 at both the first and second temperature range, while atleast one sheath hole 215 a is configured to block one or more dampingorifices 209 when within the second temperature range. It iscontemplated the device 211 can be configured for similar use outsidethe piston 205 in any suitable manner.

In certain embodiments, the sheath can be mounted to the inside of thepiston 205 on a proximal end (e.g., left as shown) in any suitablemanner (e.g., threading, rotational pin locking to prevent rotation ofsheath) and can be any suitable length in the piston cavity 207 (e.g.,shorter than the distance of the last damping hole 209, for example).However, any suitable arrangement is contemplated herein. For example,the sheath of the damping orifice blocking device 211 can be mounted tothe opposite end of the piston 205 and can be much longer to reachbeneath the damping orifices 209. In such an embodiment, the longer thesheath, the more significant the axial thermal expansion or contractionis relative to the piston 205.

In accordance with at least one aspect of this disclosure, a method forcontrolled damping of an actuator over a temperature range comprisesmodifying damping orifice flow area within the actuator as a function oftemperature to account for viscosity changes with temperature changes.Modifying the damping orifice flow area can include allowing flowthrough one or more damping orifices of a piston when within a firsttemperature range and blocking the one or more damping orifices whenwithin a second temperature range that is higher than the firsttemperature range.

In certain embodiments, blocking the one or more damping orifices whenwithin a second temperature range includes radially expanding a dampingorifice blocking device within the piston to block the one or moredamping orifices. In certain embodiments can include blocking the one ormore damping orifices when within a second temperature range includesaxially expanding a damping orifice blocking device within the piston toblock the one or more damping orifices.

Traditional actuators for RATs are designed for meeting deployment timerequirements at the coldest operational temperature and for meetingforce load requirements at the warmest operational temperature.Embodiments of this disclosure solve this issue. For example, certainblocking devices within pistons can expand faster than pistons, so in awarm temperature, embodiments close damping orifices which reduces flowarea for the hydraulic fluid and reduces maximum force experiencedwithout sacrificing speed at a cold temperature.

Accordingly, embodiments cause a portion of the damping orifices to bepartially or fully closed when the hydraulic fluid is warm so that thecombined damping orifice area is reduced. At cold temperatures theseorifices can be open such that the combined damping orifice area isincreased. Using proper sizing, embodiments can compensate for thechange in viscosity of the hydraulic fluid. As described above, incertain embodiments, the mechanism of the orifices opening and closingat different temperatures can be accomplished through the use of twodifferent materials that have different thermal coefficients ofexpansion. Embodiments allow for more consistent deployment times acrossthe RAT operating temperature range, and as a result of this moreconsistent deployment time, the average deployment time could be slowedwhich would lead to a lower impact force at the end of RAT deployment.This reduces the mass of the actuator and/or allows lower cost ofmaterials and/or materials processing.

The methods and systems of the present disclosure, as described aboveand shown in the drawings, provide for actuators (e.g., for RATs) withsuperior properties. While the apparatus and methods of the subjectdisclosure have been shown and described with reference to embodiments,those skilled in the art will readily appreciate that changes and/ormodifications may be made thereto without departing from the spirit andscope of the subject disclosure.

What is claimed is:
 1. A ram air turbine (RAT) actuator, comprising: ahousing; a piston in operable communication with the housing; at leastone damping orifice in operable communication with the housing and thepiston, a flow area of the at least one damping orifice being alterableto adjust damping of movement between the piston and the housing inresponse to changes in viscosity of a fluid related to temperature. 2.The actuator of claim 1, wherein the housing defines a housing cavity,wherein the piston is at least partially disposed within the housingcavity of the housing in a sealing relationship with the housing,wherein the piston defines a piston cavity therein and is configured toallow the housing to move axially relative to the piston between adeployed position and a stowed position, wherein a plurality of dampingorifices are defined in the piston, wherein hydraulic fluid can flowbetween the housing cavity and the piston cavity through the pluralityof damping orifices, and wherein the actuator includes a damping orificeblocking device disposed around or within the piston and configured toallow or block flow through one or more of the damping orifices as afunction of temperature.
 3. The actuator of claim 2, wherein the dampingorifice blocking device is configured to allow flow through one or moreof the damping orifices when within a first temperature range and toblock the one or more damping orifices when within a second temperaturerange that is higher than the first temperature range.
 4. The actuatorof claim 3, wherein the piston is made from a first material and whereinthe damping orifice blocking device is made of a second materialdifferent than the first material.
 5. The actuator of claim 4, whereinthe second material of the damping orifice blocking device thermallyexpands faster than the first material of the piston.
 6. The actuator ofclaim 5, wherein the damping orifice blocking device is aluminum and thepiston is made of steel.
 7. The actuator of claim 3, wherein the pistoncavity is configured to contain the damping orifice blocking devicetherein.
 8. The actuator of claim 7, wherein the piston includes aretaining structure within the piston cavity to retain the dampingorifice blocking device between the first and second temperature range.9. The actuator of claim 8, wherein the damping orifice blocking deviceis a ring or a bimetallic spring disposed within the retaining structureconfigured to expand radially to block the one or more damping orificeswhen within the second temperature range.
 10. The actuator of claim 7,wherein the damping orifice blocking device includes a sheath disposedwithin the piston cavity and fixed at one end relative to the pistonsuch that the sheath can thermally expand axially relative to the pistonto block the one or more damping orifices when within the secondtemperature range.
 11. The actuator of claim 10, wherein the sheathincludes a plurality of sheath holes corresponding to the one or moredamping orifices such that the sheath holes align with the one or moredamping orifices when within the first temperature range and the sheaththermally expands to block the one or more damping orifices when withinthe second temperature range.
 12. The actuator of claim 2, wherein thepiston is configured to be fixed to an aircraft and the housing isconfigured to be moved relative to the piston.
 13. A method forcontrolled damping of an actuator over a temperature range, comprising:modifying a damping orifice flow area of at least one damping orificewithin the actuator as a function of temperature to counteract viscositychanges of a damping fluid related to temperature changes.
 14. Themethod of claim 13, wherein modifying the damping orifice flow areaincludes allowing flow through one or more damping orifices of a pistonwhen within a first temperature range and blocking the one or moredamping orifices when within a second temperature range that is higherthan the first temperature range.
 15. The method of claim 14, whereinblocking the one or more damping orifices when within a secondtemperature range includes radially expanding a damping orifice blockingdevice within the piston to block the one or more damping orifices. 16.The method of claim 14, wherein blocking the one or more dampingorifices when within a second temperature range includes axiallyexpanding a damping orifice blocking device within the piston to blockthe one or more damping orifices.
 17. A ram air turbine (RAT) actuator,comprising: a housing defining a housing cavity; a piston at leastpartially disposed within the housing cavity of the housing in a sealingrelationship with the housing, wherein the piston defines a pistoncavity therein and is configured to allow the housing to move axiallyrelative to the piston between a deployed position and a stowedposition, wherein a plurality of damping orifices are defined in thepiston, wherein hydraulic fluid can flow between the housing cavity andthe piston cavity through the plurality of damping orifices; and adamping orifice blocking device disposed around or within the piston andconfigured to allow or block flow through one or more of the dampingorifices as a function of temperature.